Epoxy resin containing an epoxy resin-modified silicone oil flexibilizer

ABSTRACT

An epoxy resin composition for encapsulating a semiconductor device comprises a flexibilizer obtained by pre-reaction of an epoxy resin and at least one modified silicone oil having the formula: ##STR1## where R 1 , R 3 , and R 4  are divalent organic groups; R 21 , R 22 , R 23 , R 24 , R 25 , R 26 , and R 27  are respectively selected from the group consisting of an alkyl group having from 1 to 5 carbon atoms, a hydroxyalkyl group having from 1 to 5 carbon atoms, an alkoxy group having from 1 to 5 carbon atoms, a phenyl group, and a fluorine-substituted alkyl group having from 1 to 5 carbon atoms; a is an integer from 10 to 300; and b is an integer from 2 to 10, in which 0≦b/(a+b)≦0.32, and wherein the equivalent ratio of phenolic hydroxyl groups in said modified silicone oil to epoxy groups of the epoxy resin of the flexibilizer is from 0.001 to 0.4:1; an epoxy resin other than the flexibilizer; and a curing agent.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an epoxy resin composition forencapsulating a semiconductor device, and more particularly to an epoxyresin composition for encapsulating a semiconductor device whichprovides a cured product which is capable of maintaining the moistureresistance and heat resistance of the epoxy resin and which has a lowmodulus of elasticity, a low coefficient of thermal expansion, and ahigh glass transition temperature.

2. Description of the Related Art

In recent years, semiconductor devices have tended to be provided with alarger chip area and an encapsulating resin of a lesser thickness. Atthe same time, there has been a trend toward a greater degree ofintegration. Accordingly, if a semiconductor device is encapsulated witha conventional epoxy resin composition, fatal flaws in a semiconductorpart can occur, such as a crack in the chip, the cutting of a bondingwire, the sliding of an aluminum wire, and the cracking of theencapsulating resin. This is because the conventional semiconductorencapsulating epoxy resin has been developed from the perspective ofheat resistance and moisture resistance, such that the cured productlacks flexibility and an unwanted large stress to the device can result.

Generally, there are two possible measures for reducing the stress to asemiconductor-encapsulating epoxy resin: one is to reduce the thermalstrain by decreasing the coefficient of thermal expansion of the resin,and the other is to reduce the stress due to thermal strain bydecreasing the modulus of elasticity. In addition, when viewed from theaspect of maintaining the heat resistance and moisture resistance andexpanding a temperature region having a small thermal strain, it isnecessary to set the glass transition temperature to a high level. Aflexibilizer may be added as a method of reducing the stress to a lowlevel. Conventional flexibilizers include, for instance, long-chainalkylene polyamine, polyoxy alkylene glycol, and bisphenol A-typediglycidyl ether having long-chain alkylene oxide. With the method ofreducing the modulus of elasticity of a resin by using such aflexibilizer, there is a drawback in that the drop in the glasstransition temperature is large, so that the heat resistance andhumidity resistance decline. (Refer to Japanese Patent Publication Nos.59-8718, 59-30820, and 59-226066.)

Meanwhile, to obtain flexibilizers in which the decline in humidityresistance and glass transition temperature is small, elastomer modifiedflexibilizers have been devised which are obtained from polybutadienehaving functional groups capable of reacting with an epoxy resin orphenol resin at both ends, or from a copolymer of butadiene andacrylonitrile. (Refer to Japanese Patent Publication Nos. 58-108220,58-174416, 58-184204, 62-9248, 59-113021, and 59-58024. However, theaforementioned elastomer flexibilizers have a problem in that theirflexibilizing effect disappears over time as the unsaturated bonds inthe elastomer are oxidized at high temperature and deteriorate as aresult.

In addition, a method is also known in which a silicone resin or asilicone rubber which has a low modulus of elasticity is dispersed inthe resin and is an outstanding flexibilizer in terms of electricalproperties and thermal stability at a high temperature (refer toJapanese Patent Publication Nos. 62-84147 and 56-4647). However, since asilicone resin has poor adhesive properties with respect to a metal(frame and the like), and since a silicone rubber has a weak interfacialstrength with respect to an epoxy matrix, the moisture permeability ofthe cured product is large, so that there is the problem that theproduct lacks reliability in that its moisture resistance and mechanicalstrength are low.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide an epoxyresin composition for encapsulating a semiconductor device capable ofbeing cured to a product which is heat resistant and moisture resistantand has a low modulus of elasticity, a low coefficient of thermalexpansion, and a high glass transition temperature equivalent to orhigher than that of a conventional epoxy resin composition.

To this end, according to the present invention, there is provided anepoxy resin composition for encapsulating a semiconductor devicecomprising: a flexibilizer obtained by pre-reaction of an epoxy resinand at least one kind of modified silicone oil having the formula:##STR2## where R₁, R₃, and R₄ are divalent organic groups; R₂₁, R₂₂,R₂₃, R₂₄, R₂₅, R₂₆, and R₂₇ are respectively one kind selected from thegroup consisting of an alkyl group having from 1 to 5 carbon atoms, ahydroxyalkyl group having from 1 to 5 carbon atoms, an alkoxy grouphaving from 1 to 5 carbon atoms, a phenyl group, and afluorine-substituted alkyl group having from 1 to 5 carbon atoms; a isan integer from 10 to 300; b is an integer from 0 to 10, in which0≦b/(a+b)≦0.32; an epoxy resin; and a curing agent.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As the epoxy resin which is used as a chief material of a composition inaccordance with a first embodiment of the invention, it is possible tocite, for instance, multifunctional epoxy resins such as acresol-novolak-type epoxy resin, a phenol-novolak-type epoxy resin, analkyl benzene-modified phenol-novolak-type epoxy resin, a halogenatedphenol-novolak-type epoxy resin, a bisphenol A-novolak-type epoxy resin,and tris(glycidoxyphenyl) methane. However, the epoxy resin should notbe restricted to the above, and they may be used singly, or two or morekinds of them may be used in combination.

In addition, the epoxy resin which is reacted with the modified siliconeoil and the other epoxy resins the may be used in compositions accordingto the invention may be of the same kind or different kinds.

As a curing agent for the epoxy resin composition in accordance with thepresent invention, it is possible to cite phenol-novolak curing agentsfor a phenol-novolak resin, a cresol-novolak resin, an alkyl modifiedphenol resin, a bisphenol A-novolak resin, and a multifunctional phenolresin such as tris(hydroxyphenyl) methane. However, the curing agentshould not be restricted to these curing agents. The usage is notrestricted to the use of a single curing agent, and two or more kindscan be used in combination.

In addition, in accordance with the present invention, it is possible toadd, as required, such additives as accelerator (catalyst), inorganicfiller, internal mold releasing agent, surface treating agent, pigment,flame retardant, and antioxidant.

An accelerator is not restricted insofar as it is an ordinary catalyst,and, as specific examples, it is possible to cite phosphoric compoundstypified by phosphines such as triphenylphosphine, imidazoles such as2-methyl-imidazole and 2-ethyl-4-methylimidazole, tertiary amines,1,8-diazabicyclo(5,4,0)undecen-7, and organic salts thereof. They may beused singly or in combination. As for an amount to be added, 1% (weight%, abbreviated as % hereinafter) or less in the encapsulating resincomposition is desirable. If the amount is 1% or more, gelation takesplace too quickly, making it difficult to effect molding.

As for inorganic fillers, it is possible to cite natural silica,synthetic silica, pulverized quartz powders such as pulverized silicaand globular silica in terms of the configuration, as well as talc,mica, silicon nitrides, and alumina. However, the inorganic fillers arenot confined to the aforementioned ones. In addition, they may be usedsingly, or two or more kinds may be used in combination. An amount ofinorganic filler to be added is preferably 250-1300 parts (parts byweight, abbreviated as parts herreinafter) with respect to 100 parts ofan epoxy resin. If the amount is less than 250 parts, the strength islow, and trouble occurs in terms of heat resistance and thermal shockresistance. If the amount is more than 1300 parts, fluidity is poor,making it difficult to effect molding.

In addition, it is possible to employ mold releasing agent such as afatty acid and its metal salts, natural wax, synthetic wax, a surfacetreating agent, a pigment such as carbon black, a fire retardant such asantimony trioxide, and an antioxidant.

A modified silicone oil in accordance with the present invention isexpressed by the general formula: ##STR3## In Formula (1), R₁, R₃, andR₄ are divalent organic groups; R₂₁, R₂₂, R₂₄, R₂₅, R₂₆, and R₂₇ arerespectively one kind selected from the group consisting of an alkylgroup having from 1 to 5 carbon atoms, a hydroxyalkyl group having from1 to 5 carbon atoms, an alkoxy group having from 1 to 5 carbon atoms, aphenyl group, and a fluorine-substituted alkyl group having from 1 to 5carbon atoms; a is an integer from 10 to 300; b is an integer from 0 to10, in which 0≦b/(a+b)≦0.32.

R₁, R₃, and R₄ include, for instance, divalent saturated hydrocarbongroups such as methylene, ethylene, trimethylene, tetramethylene, andpropylene, divalent groups including ether bonds from 0 to 10 carbonatoms, a phenylene group, divalent alicyclic hydrocarbon group, and aheterocyclic group. R₁, R₃, and R₄ may be identical or different. Inaddition, the number of siloxane units (a in Formula (1)) is an integerfrom 10 to 300, and if the value is smaller than 10, the amount of thereduction of the modulus of elasticity falls, while, if the value a isgreater than 300, reactivity with an epoxy resin becomes extremelysmall, and the interfacial strength is weak, so that flaws can occur inproperties such as crack resistance. For that reason, in the case of asilicone having a large value a, it is desirable to provide phenolichydroxyl groups in the molecule in addition to both terminals. In thatcase, the value b is an integer from 0 to 10, and 0≦b/(a+b)≦0.32. If thevalue b/(a+b) becomes greater than 0.32, gelation occurs at the time ofpre-reaction with the epoxy resin, and a stable flexibilizer cannot beobtained. In addition, the aforementioned silicone oils may be usedsingly, or two or more kinds may be used in combination.

In the pre-reaction for obtaining a flexibilizer by reacting theaforementioned modified silicone oil and the epoxy resin, the equivalentratio of the phenolic hydroxyl groups in the phenol modified siliconeoil to the epoxy groups of the epoxy resin (phenolic hydroxylgroups/epoxy groups) is preferably 0.4 or less. If the ratio is greaterthan 0.4, gelation occurs in pre-reaction with the epoxy resin, and astable flexibilizer cannot be obtained. As the catalyst forpre-reaction, it is preferable to add 3 parts or less with respect to100 parts of the silicone oil. A pre-reaction product thus synthesizedis preferably one in which 70% or more of the phenolic hydroxyl groupsin the silicone oil have reacted with the epoxy groups of the epoxyresin. In the case of a pre-reaction product in which less than 70% arereacted, drawbacks occur in that a decline in the strength as asemiconductor-encapsulating material becomes large, and that a reductionin weight becomes large in a case where the cured product is held for along period of time at a high temperature.

As for the semiconductor-encapsulating epoxy resin composition inaccordance with this embodiment, if it is assumed that the amount of themodified silicone oil added is [A], and organic components of the epoxyresin to be reacted with the modified silicone oil, other epoxy resins,a curing agent, etc. are [B], it is preferred that [A]/{[A]+[B]} is from3 to 20%, i.e., 0.03 to 0.2. If the ratio is below 3% (0.03), the effectof lowering the modulus of elasticity of the molded product is small,and an increase in the glass transition temperature is small. On theother hand, if the ratio exceeds 20% (0.2), a decline in the mechanicalstrength becomes appreciably large.

In the present invention, a copolymer obtained by pre-reaction of thesilicone oil and the epoxy resin has a silicone polymer, which is aflexibilizing component, preliminarily bonded therein. This siliconepolymer is obtained through arbitrary reaction of phenolic hydroxylgroups located at both terminals of the silicone polymer or at bothterminals and inside the molecule on the one hand, and epoxy groups inthe epoxy resin on the other. This silicone polymer is capable oftoughening the interface between the silicone and the matrix.

Hereafter, a description will be given of an epoxy resin composition inaccordance with a second embodiment of the present invention. As for anepoxy resin serving as a main agent and a curing agent which areemployed in this epoxy resin composition, those described in theabove-described first embodiment are used.

As for flexibilizers, the following two types of flexibilizer are used:a flexibilizer (hereafter referred to as the flexibilizer (A))constituted by a pre-reaction product of a modified silicone oil(hereafter referred to as the modified silicone oil (a)) havinghydroxyphenyl groups; and a flexibilizer (hereafter referred to as theflexibilizer (B)) constituted by a pre-reaction product of a modifiedsilicone oil (hereafter referred to as the modified silicone oil (b))having epoxy groups and a phenol resin.

The flexibilizer (A) is obtained by allowing reaction (pre-reaction) totake place in a nitrogen atmosphere by using the modified silicone oil(a), the epoxy resin, and catalysts including an amine compound, animidazole compound, and a phosphoric compound.

The modified silicone oil (a) may have hydroxyphenyl groups at theterminals of the molecule and may contain them inside the molecularchain.

The hydroxyl group equivalent of the hydroxyphenyl groups of themodified silicone oil (a) is preferably from 500 to 30,000, morepreferably from 1,000 to 10,000. In addition, the number ofhydroxyphenyl groups per molecule is preferably from 1 to 15. In thecase of the modified silicone oil (a) having hydroxyphenyl groups insidethe molecular chain, from 1 to 10 hydroxyphenyl groups are preferablycontained in the molecule. If the hydroxyl group equivalent of thehydroxyphenyl groups and the number of hydroxyphenyl groups per moleculeexceed the aforementioned ranges, if the number of hydroxyphenyl groupsis small, there is a tendency that reaction fails to proceedsufficiently at the time of reaction with the novolak-type epoxy resin,whereas, if the number of hydroxyphenyl groups is large, gelation isprone to occur during reaction.

In addition, the modified silicone oil (a) is one which is constitutedby a siloxane skeleton and, as groups bonded to silicon atom, has one ormore kinds selected from an alkyl group having from 1 to 5 carbon atoms,an alkoxy group having from 1 to 5 carbon atoms, a phenyl group, and afluorine-substituted alkyl group having from 1 to 5 carbon atoms.

As specific examples of an epoxy resin to be reacted with the modifiedsilicone oil (a), it is possible to cite the same epoxy resins used asthe above-described main agent. In addition, the epoxy resin to bereacted with the modified silicone oil (a) and the epoxy resin used as amain agent may be of the same kind or different kinds.

The mixing ratio between the modified silicone oil (a) and the epoxyresin in the above-described reaction (pre-reaction) is preferably suchthat the equivalent ratio of the hydroxyl groups of the modifiedsilicone oil (a) to the epoxy groups of the epoxy resin (phenolichydroxyl groups/epoxy groups) is from 0.001 to 0.4. In particular, in acase where the modified silicone oil (a) having hydroxyphenyl groups atboth terminals of the molecule is used, a ratio of from 0.01 to 0.3 ispreferable.

If the equivalent ratio of the hydroxyl groups of the modified siliconeoil (a) to the epoxy groups of the epoxy resin is smaller than 0.001,the proportion of the modified silicone oil component in theflexibilizer (A) becomes small, so that the flexibilizing effect tendsnot to be exhibited sufficiently. On the other hand, if the ratio ismade greater than 0.4, gelation is prone to occur during pre-reaction,and there is a tendency that a stable flexibilizer (A) is difficult toobtain.

As specific examples of amine compounds used as catalysts, it ispossible to cite, for example, N-methyl piperazine andhydroxymethylpiperazine. As specific examples of imidazole compounds, itis possible to cite such as 2-ethyl-4-methylimidazole, and2-methylimidazole, benzimidazole. As for specific examples of phosphoriccompounds, it is possible to cite such as trialkylphosphine,triphenylphosphine, alkyldiphenylphosphine, and dialkylphenylphosphine.

The flexibilizer (A) thus prepared is one in which 70% or more,preferably 90% or more, of the hydroxyl groups of the modified siliconeoil (a) are reacted with the epoxy groups of the epoxy resin inpre-reaction so as to provide excellent heat resistance and highmoisture resistance.

The flexibilizer (B) is obtained by allowing reaction (pre-reaction) totake place in a nitrogen atmosphere by using the modified silicone oil(b), the phenol resin, and catalysts including an amine compound, animidazole compound, a phosphoric compound, and the like.

The modified silicone oil (b) may have epoxy groups at the terminals ofthe molecule or inside the molecular chain.

The epoxy equivalent of the modified silicone oil (b) is preferably from500 to 40,000, more preferably from 500 to 20,000. The number of epoxygroups per molecule is preferably from 1 to 20, and in the case of themodified silicone oil (b) having epoxy groups inside the molecularchain, from 1 to 8 epoxy groups may be contained in the molecule. If theepoxy equivalent and the number of epoxy groups per molecule deviatesfrom the aforementioned ranges, if the number of epoxy groups is small,there is a tendency that reaction fails to proceed sufficiently at thetime of reaction with the novolak-type epoxy resin, whereas, if thenumber of epoxy groups is large, gelation is prone to occur duringreaction.

In addition, the modified silicone oil (b) is one which is constitutedby a siloxane skeleton and, as groups bonded to silicon atom, has one ormore kinds selected from an alkyl group having from 1 to 5 carbon atoms,an alkoxy group having from 1 to 5 carbon atoms, a phenyl group, and afluorine-substituted alkyl group having from 1 to 5 carbon atoms.

As specific examples of phenol resin to be reacted with the modifiedsilicone oil (b), it is possible to cite the same phenol resins used asthe above-described main curing agent. In addition, the phenol resin tobe reacted with the modified silicone oil (b) and the phenol resin usedas the curing agent may be of the same kind or different kinds.

The compounding ratio between the modified silicone oil (b) and thephenol resin in the above-described reaction (pre-reaction) ispreferably such that the equivalent ratio of the epoxy groups of themodified silicone oil (b) to the hydroxyl groups of the phenol resin(epoxy groups/phenolic hydroxyl groups) is from 0.001 to 0.3.Particularly in the case where the modified silicone oil (b) havingepoxy groups at both terminals of the molecule is used, a ratio from0.01 to 0.3 is preferable.

If the equivalent ratio of the epoxy groups of the modified silicone oil(b) to the hydroxyl groups of the phenol resin is smaller than 0.001,the proportion of the modified silicone oil component in theflexibilizer (B) becomes small, so that the flexibilizing effect tendsnot to be exhibited sufficiently. On the other hand, if the ratio ismade greater than 0.3, gelation is prone to occur during pre-reaction,and there is a tendency that a stable flexibilizer (B) is difficult toobtain.

As specific examples of amine compounds, imidazole compounds, andphosphoric compounds that are used as catalysts, it is possible to citeones similar to those used in the preparation of the flexibilizer (A).

In the light of heat resistance and moisture resistance, it is preferredthat the flexibilizer (B) thus prepared is one in which 70% or more,preferably 90% or more, of the epoxy groups of the modified silicone oil(b) are reacted with the hydroxyl groups of the phenol resin inpre-reaction.

The mixing ratio between the flexibilizer (A) and the flexibilizer (B)in the composition in accordance with this embodiment is such that if itis assumed that the total amount (weight) of the modified silicone oil(a) and the modified silicone oil (b) added is [C] and that the amount(weight) of organic components of the epoxy resin and the phenol resinfor reaction with the modified silicone oil (a) and the modifiedsilicone oil (b), the other epoxy resins, and the curing agent is [D],then [C]/{[C]+[D]}is from 0.03 to 0.3, preferably from 0.05 to 0.2. Ifthis value is less than 0.03, the effect of reducing the modulus ofelasticity of a molded product obtained and an increase in the glasstransition temperature are small, and a decline in the expansioncoefficient tends to be small. On the other hand, if the value exceeds0.3, the mechanical strength disadvantageously declines.

In the composition according to this embodiment, it is preferable in thelight of the object of the present invention that the ratio (epoxygroups/phenolic hydroxyl groups) between the total of the equivalent ofthe epoxy groups of the epoxy resin used as a main agent and the epoxygroups of the flexibilizer (A) on the one hand, and the total of theequivalent of the phenolic hydroxyl groups contained in the curing agentand the flexibilizer (B) is in the range of from 0.7 to 1.3.

The curing agents used in this embodiment are not particularlyrestricted insofar as they are catalysts that are generally used. Asspecific examples, it is possible to cite, for instance, phosphoriccompounds typified by phosphines such as triphenylphosphine, imidazolessuch as 2-mehtylimidazole and 2-ethyl-4-methylimidasole, tertiaryamines, 1,8-diazabicyclo(5,4,0)undecen-7, and organic salts thereof. Asingle one of them may be used, or two or more of them may be used incombination. As for the amount of the accelerator added, from 0.03 to 1%in the composition in accordance with this embodiment is preferable, andfrom 0.05 to 0.7% is more preferable. If the amount of the acceleratoradded exceeds 1%, gelation is prone to take place too quickly, making itdifficult to form a cured product. If said amount is less than 0.03%,curing tends to be carried out insufficiently.

The inorganic filler used in this embodiment is not particularlyrestricted, and, as specific examples, it is possible to cite pulverizedquartz powders such as pulverized silica and globular silica obtainedfrom natural silica or synthetic silica as well as talc, mica, siliconnitride, alumina, and the like. A single one of them may be used, or twoor more kinds of them may be used in combination. The amount of theinorganic filler used is preferably from 250 to 1,300 parts, morepreferably 400 to 1,100 parts with respect to a total of 100 parts ofthe epoxy resin used in the composition in accordance with thisembodiment. If the amount used is less than 250 parts, the strength,heat resistance, and resistance to thermal shock of the cured objectobtained decline, whereas, if the amount exceeds 1,300 parts, thefluidity of the composition declines, so that it tends to be difficultto effect molding.

A mold releasing agent (internal mold releasing agent) used in thisembodiment is not particularly restricted, and as specific examplesthereof, it is possible to cite a fatty acid and its metal salts,natural wax, and synthetic wax. The amount of the releasing agent usedis preferably from 1 to 10 parts, more preferably from 3-7 parts, withrespect to 100 parts of the epoxy resin.

A surface treating agent used in this embodiment is not particularlyconfined, and as specific examples thereof, it is possible to cite, forinstance, vinyltrimethoxysilane, vinyltriethoxysilane,N(2-aminoethyl)3-aminopropylmethyldimethoxysilane,3-aminopropylethoxysilane, 3-glycidoxypropyl trimethoxysilane,3-glycidoxypropylmethyldimethoxysilane. The amount of the surfacetreating agent used is preferably from 1 to 20 parts, more preferablyfrom 3 to 15 parts, with respect to 100 parts of epoxy resin.

Furthermore, a pigment such as carbon black, a flame retardant such asantimony trioxide, an antioxidant may be compounded in the compositionof this embodiment, as required.

The composition of this embodiment can be prepared by mixing theaforementioned epoxy resin, curing agent, flexibilizer (A), flexibilizer(B), accelerator, filler, mold-releasing agent, surface-treating agent,and other required components in accordance with a conventional method(e.g. heat roll method).

The semiconductor-encapsulating epoxy resin composition in thisembodiment is characterized by the combined use of the flexibilizer (A)and the flexibilizer (B), and since silicone oil serving as aflexibilizing component is introduced into both the epoxy resin, i.e.,the chief material, and the phenol resin, i.e., the curing agent, thedispersibility of the silicone component in the matrix can be improved,and the heat resistance and moisture resistance can be improved.

A more detailed description will now be given of the epoxy resincomposition in accordance with the first embodiment of the presentinvention on the basis of Examples 1 to 7 and Comparative Examples 1, 2.

EXAMPLE 1

50 parts of a modified silicone oil of the following general formula:##STR4## and has an average molecular weight of 1,200 and a phenolichydroxyl group equivalent of 630 was reacted with 100 parts of amultifunctional epoxy resin (brandname: EPPN 502, made by Nippon KayakuCo., Ltd.) having an epoxy equivalent (W. P. E.) of 170 and 1 part oftriphenylphosphine in an nitrogen atmosphere at 140° C. to obtain aflexibilizer (1).

Then, 81 parts of the epoxy resin (EPPN-502) used in the flexibilizer(1), 10 parts of a phenol bromide novolak epoxy resin (brandname:BREN-S, made by Nippon Kayaku Co., Ltd.) having an epoxy equivalent (W.P. E.) of 280, 66 parts by weight of a phenol novolak resin (brandname:PSF-4261, made by Gunei Chemical Industry Co., Ltd.) which has aphenolic hydroxyl group equivalent of 105 and is added so that the totalepoxy equivalent and the total phenolic hydroxyl group equivalent of theaforementioned epoxy resin become equal, 29 parts of the aforementionedflexibilizer (1), 1 part of triphenylphosphine (TPP), a silane couplingagent, an internal mold-releasing agent, molten silica powders used asan inorganic filler, antimony trioxide, and a coloring agent were mixedin loadings shown in Table 1, and were heated to facilitate mixing. Asemiconductor-encapsulating epoxy resin composition in accordance withthe first embodiment of the present invention was thereby obtained.

EXAMPLES 2, 3

A semiconductor-encapsulating epoxy resin composition was obtained inthe same way as Example 1 except that the amounts of the flexibilizer(1) obtained in Example 1 and other components were varied, as shown inTable 1.

EXAMPLE 4

A flexibilizer (2) was obtained in the same way as Example 1 by using amodified silicone oil of the following formula: ##STR5## having anaverage molecular weight of 4,500 and a phenolic hydroxyl groupequivalent of 2,200 instead of the modified silicone oil used inExample 1. Then, a semiconductor-encapsulating epoxy resin compositionwas obtained in the same way as Example 1 except that the amounts of theflexibilizer (2) and other components were varied, as shown in Table 1.

EXAMPLE 5

A flexibilizer (3) was obtained in the same way as Example 1 by using amodified silicone oil of the following formula: ##STR6## having anaverage molecular weight of 11,000 and a phenolic hydroxyl groupequivalent of 5,600 instead of the modified silicone oil used inExample 1. Then, a semiconductor-encapsulating epoxy resin compositionwas obtained in the same way as Example 1 except that the amounts of theflexibilizer (3) and other components were varied, as shown in Table 1.

EXAMPLE 6

A flexibilizer (4) was obtained in the same way as Example 1 by using amodified silicone oil of the following formula: ##STR7## having anaverage molecular weight of 11,000 and a phenolic hydroxyl groupequivalent of 2,100 instead of the modified silicone oil used inExample 1. Then, a semiconductor-encapsulating epoxy resin compositionwas obtained in the same way as Example 1 except that the amounts of theflexibilizer (4) and other components were varied, as shown in Table 1.

EXAMPLE 7

A semiconductor-encapsulating epoxy resin composition was obtained bysetting the amount of the flexibilizer (4) synthesized in Example 6 andthe amounts of other organic components in the same way as Example 6except that 1,200 parts of an inorganic filler was mixed in.

COMPARATIVE EXAMPLE 1

An epoxy resin composition was obtained by using a silicone oilflexibilizer (5) having a phenolic hydroxyl group equivalent of 210 andmixing the components with the loadings shown in Table 1.

COMPARATIVE EXAMPLE 2

An epoxy resin composition was obtained without using any flexibilizerand by mixing the components with the loadings shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________                  Phenol              In-      Results of Evaluation                            Curing              or-                Coef-                    Epoxy Resin   Agent               gan-          Glass                                                                              ficient                  (parts)       (Parts)             ic       Modulus                                                                            Transi-                                                                            of                                                                                  Heatmal            EPPN          (Hydroxyl                                                                           Cata-         fil-     of Elas-                                                                           tion Ex-   Cycle              502      BREN-S                                                                             Group lyst                                                                              Flexibilizer                                                                            ler Other                                                                              ticity                                                                             Temper-                                                                            pansion                                                                             Failure            (W.P.E.  (W.P.E.                                                                            Equivalent                                                                          (Parts)                                                                           (Parts)   (Par-                                                                             Additive                                                                           (kg/ ature                                                                              10.sup.6                                                                            Rate               170)     280) 105)  TPP 1 2 3 4 5 ts) (Parts)                                                                            mm.sup.2)                                                                          (°C.)                                                                       (°C..sup.-1)                                                                 (%)                __________________________________________________________________________    Ex-                                                                           amples                                                                        1   81   10   66    1   29                                                                              --                                                                              --                                                                              --                                                                              --                                                                              730 13   1700 206  16    20                 2   60   10   66    1   61                                                                              --                                                                              --                                                                              --                                                                              --                                                                              770 13   1490 214  13    0                  3   36   10   66    1   96                                                                              --                                                                              --                                                                              --                                                                              --                                                                              810 13   1310 220  12    0                  4   60   10   66    1   --                                                                              61                                                                              --                                                                              --                                                                              --                                                                              770 13   1480 217  13    0                  5   60   10   66    1   --                                                                              --                                                                              61                                                                              --                                                                              --                                                                              770 13   1450 215  13    0                  6   60   10   66    1   --                                                                              --                                                                              --                                                                              61                                                                              --                                                                              770 13   1470 218  13    0                  7   60   10   66    1   --                                                                              --                                                                              --                                                                              61                                                                              --                                                                              1200                                                                              13   1610 222  11    0                  Com-                                                                          para-                                                                         tive                                                                          Ex-                                                                           amples                                                                        1   60   10   66    1   --                                                                              --                                                                              --                                                                              --                                                                              61                                                                              770 13   1810 207  19    60                 2   100  10   66    1   --                                                                              --                                                                              --                                                                              --                                                                              --                                                                              694 13   1950 204  17    100                __________________________________________________________________________

Properties Test

Cured testpieces of epoxy resin compositions of the above-describedExamples 1 to 6 and Comparative Examples 1, 2 were prepared, and themechanical strength (JIS K 6911), the glass transition temperature, thecoefficient of thermal expansion, and the package cracking propertiesafter 100 heat cycles at -196° C.×30 sec to 260° C.×30 sec were measuredfor the respective testpieces. The results are shown in Table 1. As isapparent from Table 1, it can be appreciated that the cured products ofthe semiconductor-encapsulating epoxy resin compositions in accordancewith the examples of the present invention exhibit high thermalresistances, low coefficients of thermal expansion, and low moduli ofelasticity, attain glass transition temperatures equivalent to or higherthan the conventional examples, possess moisture resistance by virtue ofepoxy resin components, and thus can be used suitably for encapsulatingsemiconductor devices.

Next, a more specific description will be given of epoxy resincompositions in accordance with the second embodiment of the presentinvention on the basis of Examples 8 to 23 and Comparative Examples 3 to5, but the present invention is not confined to these Examples.

EXAMPLE 8

50 parts of a modified silicone oil having a hydroxyl group equivalentof 1,100, hydroxyphenyl groups at both terminals of the molecular chain,and a polydimethylsiloxane skeleton, 100 parts of a novolak-type epoxyresin (EPPN 501 made by Nippon Kayaku Co., Ltd., epoxy equivalent (W. P.E.: 165), and 1 part of triphenylphosphine were reacted at 150° C. forabout 20 hours while nitrogen was blowing into the mixture.Consequently, a pre-reaction product (plasticizer (A-1)) of the modifiedsilicone oil having hydroxyphenyl groups at both terminals of themolecule and the epoxy resin. The reaction rate was 97%.

50 parts of a modified silicone oil having an epoxy equivalent of 1,300,epoxy groups at both terminals of the molecule, and apolydimethylsiloxane skeleton, 100 parts of a novolak-type phenol resin(PSF-4261 made by Gunei Chemical Industry Co., Ltd., hydroxyl groupequivalent: 106) (equivalent ratio of epoxy groups to phenolic hydroxylgroups: 0.04), and 1 part of triphenylphosphine were reacted at 150° C.while nitrogen was being blown into the mixture. Consequently, apre-reaction product (plasticizer (B-1)) of the modified silicone oilhaving epoxy groups at both terminals of the molecular chain and thephenol resin was obtained. The reaction rate was 95%.

The epoxy resin (EPPN-501), i.e., the chief material, the phenol bromidenovolak-type epoxy resin (BREN-S made by Nippon Kayaku Co., Ltd.), thecuring agent phenol novolak resin (PSF-4261), the accelerator(triphenylphosphine), the plasticizer (A-1), the flexibilizer (B-1),molten silica (RD-8 made by Tatsumori Co., Ltd.), antimony trioxide, andother materials (silane coupling agent, internal mold-releasing agent,and coloring agent) were mixed with the ratio shown in Table 2, werethen kneaded by a heat roll, thereby obtaining asemiconductor-encapsulating epoxy resin composition.

The resultant composition was subjected to transfer molding at 175° C.for two minutes, and cured testpieces were prepared.

Using the cured testpieces thus obtained, measurement was made of themechanical properties (JIS K 6911), the glass transition temperature,the coefficient of thermal expansion, and the package cracking propertyafter 100 heat cycles at -196° C.×30 sec to 260° C.×30 sec. The resultsare shown in Table 2.

EXAMPLES 9-11

70 parts of a modified silicone oil having an epoxy equivalent of 2,300,epoxy groups at both terminals of the molecular chain, and apolydimethylsiloxane skeleton, 100 parts of the phenol novolak resin(PSF-4261) (equivalent ratio of epoxy groups to phenolic hydroxylgroups: 0.03), and 1 part of triphenylphosphine were reacted in the sameway as Example 8, thereby obtaining a flexibilizer (B-2). The reactionrate was 95%.

100 parts of a modified silicone oil having an epoxy equivalent of6,200, epoxy groups at both terminals of the molecular chain, and apolydimethylsiloxane skeleton, 100 parts of the phenol novolak resin(PSF-4261) (equivalent ratio of epoxy groups to phenolic hydroxylgroups: 0.02), and 1.2 parts of triphenylphosphine were reacted in thesame way as Example 8, thereby obtaining a flexibilizer (B-3). Thereaction rate was 94%.

90 parts of a modified silicone oil having an epoxy equivalent of 3,500,epoxy groups (about 4 per molecule) at both terminals and the inside ofthe molecular chain, and a polydimethylsiloxane skeleton, 100 parts ofthe phenol novolak resin (PSF-4261) (equivalent ratio of epoxy groups tophenolic hydroxyl groups: 0.03), and 1 part of triphenylphosphine werereacted in the same way as Example 8, thereby obtaining a flexibilizer(B-4). The reaction rate was 85%.

The flexibilizer (A-1) obtained in Example 8, the flexibilizer (B-2),the flexibilizer (B-3), and the flexibilizer (B-4) were used incombination, a semiconductor-encapsulating epoxy resin composition wasobtained in the same way as Example 8 except that the other componentswere used at the proportions shown in Table 2.

Then, in the same way as Example 8, cured testpieces were prepared andtheir properties were measured. The results are shown in Table 2.

EXAMPLES 12 TO 23

Reaction was allowed to take place in the same way as Example 8 exceptthat 80 parts of a modified silicone oil having a hydroxyl groupequivalent of 2,700, hydroxyphenyl groups at both terminals of themolecular chain, and a polydimethylsiloxane skeleton, 100 parts of theepoxy resin (EPPN-501) (equivalent ratio of phenolic hydroxyl groups toepoxy groups: 0.05), and 1 part of triphenylphosphine were used, and aflexibilizer (A-2) was thereby obtained. The reaction rate was 96%.

110 parts of a modified silicone oil having a hydroxyl group equivalentof 5,800, hydroxyphenyl groups at both terminals of the molecular chain,and a polydimethylsiloxane skeleton, 100 parts of the epoxy resin(EPPN-501) (equivalent ratio of phenolic hydroxyl groups to epoxygroups: 0.03), and 1.2 parts of triphenylphosphine were used, andreaction was allowed to take place in the same way as Example 8, therebyobtaining a flexibilizer (A-3). The reaction rate was 93%.

70 parts of a modified silicone oil having a hydroxyl group equivalentof 3,800, hydroxyphenyl groups (about 4 per molecule) at both terminalsand the inside of the molecular chain, and a polydimethylsiloxaneskeleton, 100 parts of the epoxy resin (EPPN-501) (equivalent ratio ofphenolic hydroxyl groups to epoxy groups: 0.03), and 1 part oftriphenylphosphine were used, and reaction was allowed to take place inthe same way as Example 8, thereby obtaining a flexibilizer (A-4) wasthereby obtained. The reaction rate was 92%.

The flexibilizer (B-1), the flexibilizer (B-2), the flexibilizer (B-3),and the flexibilizer (B-4), which were respectively obtained in Examples8-11, as well as the flexibilizer (A-2), the flexibilizer (A-3), and theflexibilizer (A-4) were used in combination, and asemiconductor-encapsulating epoxy resin composition was obtained in thesame way as Example 8 except that the other components were used in theproportions shown in Table 2.

Subsequently, cured testpieces were prepared in the same way as Example8, and their properties were measured. The results are shown in Table 2.

COMPARATIVE EXAMPLES 3-4

An epoxy resin composition with loadings shown in Table 2 was obtainedin the same way as Example 8, using as a flexibilizer Araldite GY 298(Comparative Example 3) made by Ciba-Geigy (Japan) Ltd. or DER 736(Comparative Example made by Dow Chemical Japan Ltd.

Subsequently, testpieces were prepared in the same way as Example 8, andtheir properties were measured. The results are shown in Table 2.

COMPARATIVE EXAMPLE 5

An epoxy resin composition with loadings shown in Table 2 was obtainedin the same way as Example 8 except that no flexibilizer was used.

Subsequently, testpieces were prepared in the same way as Example 8, andtheir properties were measured. The results are shown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________           Epoxy Resin                                                                             Phenol                                                              (Parts)   Curing                                                              EPPN      Agent (Parts)                                                       501  BREN-S                                                                             PSF4261         Flexibilizer (Parts)                                (W.P.E.                                                                            (W.P.E.                                                                            (Hydroxyl Group                                                                        Accelerator                                                                          A           B           GY PER                      164) 280) Equivalent 106)                                                                        (Parts)                                                                              A-1                                                                              A-2                                                                              A-3                                                                              A-4                                                                              B-1                                                                              B-2                                                                              B-3                                                                              B-4                                                                              298                                                                              736               __________________________________________________________________________    Examples                                                                       8     79   10   47.5     1      31.4                                                                             --       31.4                                                                             -- -- -- -- --                 9     79   10   53.5     1      31.4                                                                             -- -- -- -- 25.4                                                                             -- -- -- --                10     79   10   57.9     1      31.4                                                                             -- -- -- -- -- 20.9                                                                             -- -- --                11     79   10   56.8     1      31.4                                                                             -- -- -- -- -- -- 22.1                                                                             -- --                12     87   10   47.5     1      -- 23.6                                                                             -- -- 31.4                                                                             -- -- -- -- --                13     87   10   53.5     1      -- 23.6                                                                             -- -- -- 25.4                                                                             -- -- -- --                14     87   10   57.9     1      -- 23.6                                                                             -- -- -- -- 20.9                                                                             -- -- --                15     87   10   56.8     1      -- 23.6                                                                             -- -- -- -- -- 22.1                                                                             -- --                16     90.5 10   47.5     1      -- -- 20 -- 31.4                                                                             -- -- -- -- --                17     90.5 10   53.5     1      -- -- 20 -- -- 25.4                                                                             -- -- -- --                18     90.5 10   57.9     1      -- -- 20 -- -- -- 20.9                                                                             -- -- --                19     90.5 10   56.8     1      -- -- 20 -- -- -- -- 22.1                                                                             -- --                20     85   10   47.5     1      -- -- -- 25.4                                                                             31.4                                                                             -- -- -- -- --                21     85   10   53.5     1      -- -- -- 25.4                                                                             -- 25.4                                                                             -- -- -- --                22     85   10   57.9     1      -- -- -- 25.4                                                                             -- -- 20.9                                                                             -- -- --                23     85   10   56.8     1      -- -- -- 25.4                                                                             -- -- -- 22.1                                                                             -- --                Comparative                                                                   Examples                                                                      3      100  10   68.4     1      -- -- -- -- -- -- -- -- 21 --                4      100  10   68.4     1      -- -- -- -- -- -- -- -- -- 21                5      100  10   68.4     1      -- -- -- -- -- -- -- -- -- --                __________________________________________________________________________                            Results of Evaluation                                                                              Coefficient                                                                   of Thermal                              Inorganic                                                                             *Other Additive                                                                        Modulus of Glass Transition                                                                        Expansion ×                                                                     Heat Cycle Failure              filler (Parts)                                                                        (Parts)  Elasticity (kg/mm.sup.2)                                                                 Temperature (°C.)                                                                10.sup.6 (°C..sup.-1)                                                          Rate                     __________________________________________________________________________                                                         (%)                      Examples                                                                       8     640     13       1410       193       17      20                        9     640     13       1300       191       17      10                       10     640     13       1290       193       15      0                        11     640     13       1420       193       15      5                        12     640     13       1310       195       15      0                        13     640     13       1290       192       16      0                        14     640     13       1260       193       15      0                        15     640     13       1350       195       15      0                        16     640     13       1310       192       16      0                        17     640     13       1270       194       15      0                        18     640     13       1250       193       15      0                        19     640     13       1320       195       16      0                        20     640     13       1380       195       16      5                        21     640     13       1300       195       16      0                        22     640     13       1270       196       16      0                        23     640     13       1390       193       16      5                        Comparative                                                                   Examples                                                                      3      640     13       1440       165       19      50                       4      640     13       1450       174       20      55                       5      577     13       1820       190       18      100                      __________________________________________________________________________     *7 parts of silane coupling agent (KBM403 made by Shinetcu Chemical           Industry Co., Ltd.), 3 parts of internal moldreleasing agent (carnauba        wax), and 3 parts of coloring agent (carbon black)                       

As is apparent from Table 2, it can be appreciated that cured productsobtained from the semiconductor-encapsulating epoxy resin compositionhave high heat resistance, low coefficients of thermal expansion, andlow moduli of elasticity, and high glass transition temperaturesequivalent to or higher than those of conventional ones, and can be usedsuitably for encapsulating semiconductor devices.

What is claimed is:
 1. An epoxy resin composition for encapsulating asemiconductor device comprising:a flexibilizer obtained by pre-reactionof an epoxy resin and at least one modified silicone oil having theformula: ##STR8## where R₁, R₃, and R₄ are divalent organic groups; R₂₁,R₂₂, R₂₃, R₂₄, R₂₅, R₂₆, and R₂₇ are respectively selected from thegroup consisting of an alkyl group having from 1 to 5 carbon atoms, ahydroxyalkyl group having from to 5 carbon atoms, an alkoxy group havingfrom 1 to 5 carbon atoms, a phenyl group, and a fluorine-substitutedalkyl group having from 1 to 5 carbon atoms; a is an integer from 10 to300; b is an integer from 2 to 10, in which 0≦b/(a+b)≦0.32 wherein theequivalent ratio of phenolic hydroxyl groups in said modified siliconeoil to epoxy groups of the epoxy resin of the flexibilizer is from 0.001to 0.4:1; an epoxy resin other than the flexibilizer; and a curingagent.
 2. The composition according to claim 1 wherein 70% or more ofphenolic hydroxyl groups in said modified silicone oil are reacted withthe epoxy groups of said epoxy resin.
 3. The composition according toclaim 1 wherein the amount of said modified silicone oil added is [A],and the epoxy resin pre-reacted with said modified silicone oil, otherepoxy resin, and curing agent are [B], and [A]/{[A]+[B]}is, from 0.03 to0.2.
 4. The composition according to claim 1 wherein said epoxy resin isat least one selected from the group consisting of a cresol-novolackepoxy resin, a phenol-novolak epoxy resin, an alkyl benzene-modifiedphenol-novolak epoxy resin, a halogenated phenol-novolak-type epoxyresin, a bisphenol A-novolak epoxy resin, and tris(glycidoxyphenyl)methane.
 5. The composition according to claim 1 wherein said curingagent comprises at least one of a phenol-novolak resin, a cresol-novolakresin, an alkyl-modified phenol resin, a bisphenol A-novolak resin ortris(glycidoxyphenyl) methane.
 6. The composition according to claim 1wherein said curing agent comprises at least one phenol novolak.
 7. Thecomposition according to claim 1 further comprising an accelerator. 8.The composition according to claim 7 wherein said accelerator is atleast one selected from the group consisting of phosphines, imidazoles,tertiary amines, and organic salts thereof.
 9. The composition accordingto claim 7 wherein said accelerator comprises at least one oftriphenylphosphine, 2-methylimidazole, 2-ethyl-4-methylimidazole,1,8-diazabicyclo(5,4,0)undecen-7, and organic salts thereof.
 10. Thecomposition according to claim 7 wherein the amount of said acceleratoradded is 1 weight % or less with respect to said resin composition. 11.The composition according to claim 1 further comprising an inorganicfiller.
 12. The composition according to claim 11 wherein said inorganicfiller is at least one selected from the group consisting of naturalsilica, synthesized silica, talc, mica, silicon nitride, and alumina.13. The composition according to claim 11 wherein the amount of saidinorganic filler added is from 250 to 1,300 parts by weight with respectto 100 parts by weight of said epoxy resin.
 14. The compositionaccording to claim 1 further comprising a mold-releasing agent.
 15. Thecomposition according to claim 14 wherein said mold-releasing agent isat least one selected from the group consisting of a fatty acid andmetal salts thereof, natural wax, and synthetic wax.
 16. The compositionaccording to claim 1 further comprising a-surface-treating agent. 17.The composition according to claim 1 further comprising a flameretardant.
 18. The composition according to claim 1 further comprising apigment.
 19. The composition according to claim 1 further comprising anantioxidant.